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VET433: Cardio/Respiratory > Canine & Feline Heartworm > Flashcards

Canine & Feline Heartworm Flashcards

1
Q

what is the nematode that causes heartworm infection

A

dirofilaria immitis

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2
Q

how is dirofilaria transmitted to dogs and cats

A

mosquito vector

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3
Q

what species are more commonly affected by heartworm disease

A

dogs > cats

cats are atypical hosts

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4
Q

where is heartworm endemic

A

all lower 48 states

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5
Q

where is heartworm hyperendemic

A

SE states and mississippi river valley

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6
Q

what drugs are used for heartworm prevention in dogs and cats

A

macrocyclic lactones (ML)

ivermectin, selamectin, moxidectin, milbemycin

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7
Q

what life stage of the heartworm lifecycle do macrocyclic lactones target

A

kills L3 and early L4 larvae

does NOT kill adults

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8
Q

when should a puppy start using prevention

A

6 to 8 weeks old
use year round

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9
Q

heartworm life cycle in a dog

A
  1. mosquito ingests microfilaria from a HW infected host
  2. in the mosquito - dirofilaria grow to L3 larvae in 10 days
  3. mosquito bites a new dog and transmitted L3 larvae into the dog tissues
  4. L3 larvae grows into L4 and resides in tissues (45-65 days)
  5. L4 enters the bloodstream and develops into an adult (4-5 months)
  6. adults in the blood start producing microfilaria
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10
Q

how long post-infection does microfilaria production begin in dogs

A

6 to 7 months

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11
Q

how long do adult HWs and microfilaria live in dogs

A

adults - 5-7 years
microfilaria - 1-2 years

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12
Q

heartworm lifecycle in a cat

A
  1. mosquito ingests microfilaria from a HW infected host
  2. in the mosquito - dirofilaria grow to L3 larvae in 10 days
  3. mosquito bites a new cat and transmits L3 larvae into the cat tissues
  4. L3 larvae grows into L4 and resides in tissues (2 months)
    - cat immune system kills majority of larvae and developing adults
  5. L4 enters the bloodstream and develops into an adult (4-6 months)
  6. adults in the blood start producing microfilaria
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13
Q

how long post-infection does microfilaria production begin in cats

A

7-8 months

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14
Q

do microfilaria circulate in cats

A

rarely

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15
Q

where do adult heartworms reside in dogs

A

pulmonary arteries
majority in the caudal pulmonary vascular tree

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16
Q

what does the severity of clinical signs depend on

A
  • relative # of worms
  • duration of infection
  • host-parasite interaction
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17
Q

how does the cat immune system respond to heartworm

A

many immature adults die once they reach the pulmonary arteries

infection is typically cleared at the L4/early L5 stage

even if cleared - can still cause inflammation in the pulmonary parenchyma and bronchioles –> cough, tachypnea

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18
Q

what is the typical worm burden in cats

A

1-3 worms

causes many false negatives on antigen tests (threshold is 3 worms)

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19
Q

what is wolbachia

A

gram negative bacteria

gets released in large numbers during worm death and exacerbate acute inflammatory response + increased bronchoreactivity

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20
Q

what can occur in feline HW infections that doesn’t occur in canine infections

A

aberrant migrations - neurologic, ocular, arterial

21
Q

what heartworm test is used in dogs

A

antigen testing

high sensitivity and specificity - good screening test

22
Q

what does the antigen test detect and how early can it detect it after infection

A

adult females
must be at least 3 worms

detects antigen 6 months after infection
- earliest detectable time for puppies - 8 months old

23
Q

if a dog has a lapse in prevention for > 6 months, when should they be tested

A

now and again in 6 months

24
Q

if a dog has a lapse in prevention for <6 months, when should they be tested

A

6 months after re-starting prevention

25
Q

how often should heartworm screening be performed

A

yearly

26
Q

what is microfilaria testing

A

tests for the presence of microfilaria in the blood

variable sensitivity - mostly used as a safety net to catch false negative antigen tests

27
Q

what heartworm test is used in cats

A

antibody test

detects antibodies against antigens produced by both male and female larvae

28
Q

why can the antigen test not be used in cats

A

cats often have too small of an adult worm burden (1-3 worms) and results in high false negatives

if a cat is positive on an antigen test - guarantee the cat is positive

29
Q

when should radiographs be used in cats suspected of HW

A

cats with respiratory signs
- pulmonary pattern
- pulmonary artery enlargement
- R sided heart enlargement

30
Q

what pathology is associated with heartworm disease in dogs

A

pneumonitis - inflammation of the pulmonary parenchyma + airways

vasoconstriction and occlusion of the lumen of the pulmonary arteries

31
Q

what pathology is associated with heartworm disease in cats

A

significant pathology even in aborted or cleared disease
- pulmonary arteries
- pulmonary alveoli + parenchyma
- bronchi, bronchioles

32
Q

clinical signs of heartworm disease in dogs

A

majority are ASYMPTOMATIC or have mild cough

  • exercise intolerance
  • severe cough or respiratory distress
  • syncope
  • hemoptysis
  • R-CHF from pulmonary hypertension
  • caval syndrome
33
Q

clinical signs of heartworm disease in cats

A

larval infection: subclinical OR cough, tachypnea, dyspnea, ARDS

adult infection: self clearance (no signs) OR GI signs, respiratory signs, R sided murmurs, syncope, ARDS, sudden death

34
Q

how to treat pneumonitis from heartworm disease in dogs

A
  1. O2 supplementation
  2. steroids
    - dexSP (IV)
    - prednisolone (PO)
35
Q

how to treat heartworm disease in dogs

A
  1. doxycycline
  2. 2 to 3 dose melarsomine
  3. steroid taper after each melarsomine dose

ACTIVITY RESTRICTION

36
Q

what is the role of doxycycline in heartworm treatment

A

kills wolbachia that’s released by the worms

37
Q

what is the role of prednisone taper after melarsomine injections

A

reduces inflammation from worm death that could otherwise cause thrombosis + vascular occlusion

38
Q

melarsomine

A

kills adult L5 worms

39
Q

why is activity restriction important

A

want to avoid exacerbating pulmonary vascular and parenchymal pathology

can lead to worsening pneumonitis and pulmonary hypertension

40
Q

how to treat heartworm disease in cats

A

do NOT use melarsomine

adulticidal:
- doxycycline + ivermectin
- surgical HW extraction

at home tx:
- prevention
- prednisolone
- fluticasone inhaler
- albuterol inhaler
- +/- clopidogrel

41
Q

how to treat cats with severe respiratory distress from HW

A
  1. O2 supplementation
  2. corticosteroids (dexamethasone)
  3. bronchodilators
42
Q

what are the complications of severe heartworm disease in dogs

A
  1. pulmonary hypertension
  2. pulmonary thromboembolism
  3. R-CHF (from PH)
  4. caval syndrome
43
Q

how to diagnose and treat pulmonary hypertension

A

echocardiogram - tricuspid regurgitation velocity

treat with sildenafil

44
Q

how to diagnose and treat PTE from heartworm disease

A

supportive diagnosis - thoracic radiographs with signs of HWD and PH

treat with steroids +/- clopidogrel

45
Q

caval syndrome

A

chronic pulmonary hypertension + reduced RV function –> retrograde movement of heartworms into the RA + vena cava –> obstructs venous return –> R-CHF and reduced CO

46
Q

clinical signs of caval syndrome

A

lethargy
tachypnea
syncope
ascites
discolored urine (pigmenturia)

47
Q

treatment of caval syndrome

A

EMERGENCY
transjugular HW extraction

48
Q

how to treat R-CHF from heartworm disease in cats

A

O2 supplementation
sedation
thoracocentesis
furosemide
abdominocentesis

VET433: Cardio/Respiratory (17 decks)

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